Research On Commutation Failure Strategy Of HVDC Transmission System

Dc transmission system has a large capacity of power transmission.At the same time,it also takes into account the advantages of low transmission loss,fast transmission power regulation,rapid and flexible power flow reversal,high transmission reliability,strong asynchronous connection ability and so on.Therefore,it is widely used in long-distance and large-area power network interconnection and large-capacity transmission.China will form a large scale and complex multi-feeder dc MIDC transmission system.As the most common typical system fault of dc transmission system.Failure of phase change will cause dc voltage drop and dc current increase in a short time and other adverse factors affecting system operation: continuous failure of phase change is likely to cause dc system derate operation.Even cause valve block or pole block.With the increase of MIDC scale and the decrease of electrical distance between dc drop points,ac system fault occurs at the receiving end.Failure of simultaneous or successive commutation of multiple cycles of dc may occur: when the ac fault is serious.The failure of multiple dc commutation may result in interruption of dc power transmission.It seriously threatens the safety and stability of dc system.This paper takes the prediction and recovery strategy of HVDC transmission system phase change as the research object,and focuses on the analysis of the influence of various AC system faults on the HVDC transmission system phase change failure and the corresponding strategies.Firstly,the mechanism,harm and actual waveform of the phase-changing failure are studied,and various influencing factors of the phase-changing failure of HVDC transmission system are analyzed.Secondly,various AC system faults of Shandong power grid are simulated to analyze the scope and influence results of commutation failures caused by AC system faults.By comparing with actual commutation failures,the relationship between the electrical distance and voltage level of AC system faults and commutation failures is further analyzed.Finally,by optimizing the prediction and protection strategies of phase change failure of converter station,the phase change failure can be reduced by improving the strategies of converter control system.In addition,measures such as adjusting camera,pumped-storage power station and safety and stability control system are adopted to ensure the stability of AC grid system parameters after AC system failure,so as to prevent phase-changing failure or even HVDC transmission system locking.